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Arterial response to mild balloon injury in the normal rabbit: evidence for low proliferation rate in the adventitia.

BACKGROUND: The role of constrictive remodeling, spasm and proliferation (particularly in the adventitia) in the genesis of chronic lumen narrowing after balloon injury remains under debate. This study analyzed the time course of these components following mild injury in normal arteries. METHODS: Iliac injury was induced by balloon overstretch in 32 rabbits, sacrificed at timed intervals from day 3 to 28. Angiographic response to nitrates, morphometric, immunohistochemical and biochemical analysis were performed at each time point. RESULTS: Quantitative angiography showed a decrease in lumen diameter and no change in response to nitrates over time. On morphometric analysis, remodeling was usually constrictive, appeared as early as day 3 and was responsible for 69+/-14% of the histologic lumen area stenosis at day 28. Constrictive remodeling was correlated negatively to intimal hyperplasia (r= 0.51, P< 0.002) and positively to the lumen area stenosis (r= 0.92, P< 0.0001). Macrophages (labeled by anti-RAM 11 antibodies) were very rare at all time points. Immunohistochemistry identified a high rate of proliferating smooth muscle cells in the media (13+/-7%) and intima (49+/-8%) at day 7, which decreased rapidly. Proliferating cells in the adventitia were rare (3+/-2% at day 7). The number of proliferating cells was time-dependent (r= 0.82, P< 0.0001) and related to cyclin A mRNA measured by reverse transcription-polymerase chain reaction (r= 0.84, P< 0.0001). CONCLUSIONS: In this model, luminal loss was mainly caused by constrictive remodeling rather than intimal hyperplasia. Constrictive remodeling appeared early and was not time-dependent. Macrophages, spasm and adventitial proliferation did not contribute to this constrictive remodeling.

Angioplasty, Balloon↗

Direct action of norepinephrine on aortic baroreceptors of rat adventitia.

The adventitia of the rat aortic arch, with the depressor nerve intact, was separated from the underlying media to obtain a preparation in which the direct effects of norepinephrine on baroreceptor discharge could be examined free of smooth muscle effects. Cyclic stretch was applied to the adventitia to evoke discharge in single aortic baroreceptor fibers. Norepinephrine and phenylephrine in concentrations of 10(-7) to 10(-5) M increased baroreceptor discharge. No effect on discharge was seen with isoproterenol. Phentolamine but not propranolol blocked the increase in discharge produced by norepinephrine. An alpha-adrenergic modulation of baroreceptor discharge that is not dependent on smooth muscle tension has been demonstrated.

Animals↗

Adventitia-dependent relaxations of canine basilar arteries transduced with recombinant eNOS gene.

We recently reported that expression of recombinant endothelial nitric oxide (NO) synthase (eNOS) gene in adventitial fibroblasts restores NO formation in canine cerebral arteries without endothelium in response to bradykinin ex vivo and in vivo. The present study was designed to further characterize the stimuli that can activate recombinant eNOS enzyme expressed in the adventitia of cerebral arteries. To stimulate recombinant eNOS, we used serum (0. 1-10%), substance P (10(-11)-3 x 10(-9) M), and ANG II (10(-7)-10(-5) M) because they increase intracellular calcium concentrations in fibroblasts. Endothelium-denuded segments of canine basilar arteries were incubated with an adenoviral vector encoding beta-galactosidase gene or eNOS gene for 30 min at 37 degrees C. After 24 h, vasomotor activity and cGMP formation in eNOS or beta-galactosidase arteries were examined by isometric force recording and by radioimmunoassay, respectively. In control arteries and beta-galactosidase gene-transduced arteries, serum caused concentration-dependent contractions, whereas in recombinant eNOS gene-transduced arteries, serum produced concentration-dependent relaxations. Substance P and ANG II had no effect on vascular tone in control and beta-galactosidase arteries but caused concentration-dependent relaxations as well as a significant increase in cGMP levels in eNOS arteries. These relaxations were blocked by the NOS inhibitor NG-nitro-L-arginine methyl ester. Chemical treatment or mechanical inactivation of adventitial function significantly attenuated substance P-induced relaxations and ANG II-induced relaxations. These findings demonstrate that serum, substance P, and ANG II cause adventitia-dependent relaxations in cerebral arteries expressing the recombinant eNOS gene. This mechanism of vasodilatation may have beneficial effects in the prevention and treatment of vascular disorders characterized by the diminished bioavailability of NO, such as cerebral vasospasm.

Angiotensin II↗

Adventitia-derived nitric oxide in rat aortas exposed to endotoxin: cell origin and functional consequences.

The role of adventitial cells in bacterial lipopolysaccharide (LPS)-induced vascular nitric oxide (NO) overproduction has been largely ignored. In rat aortas exposed to LPS in vitro or in vivo, it was found that adventitia contained the major part of NO synthase (NOS)-2 protein (Western blot and immunohistochemistry) and generated the largest amount of NO (electron paramagnetic resonance spin trapping). NOS-2 immunoreactive cells were mainly resident macrophages at an early stage (5 h, in vitro or in vivo) and fibroblasts at a later stage (20 h, in vitro). Adventitial NOS-2 activity largely accounted for 1) the relaxing effect of L-arginine in rings exposed to LPS in vivo, 2) generation of an "NO store" revealed by N-acetylcysteine-induced relaxation, and 3) formation of protein-bound dinitrosyl iron complexes in the medial layer of aortic rings exposed to LPS in vitro. In conclusion, the adventitia is a powerful source of NO triggered by LPS in the rat aorta. This novel source of NO has an important impact on smooth muscle function and might be implicated in various inflammatory diseases.

Animals↗

Modulation of baroreceptor activity by gene transfer of nitric oxide synthase to carotid sinus adventitia.

Administration of nitric oxide (NO) or NO donors to isolated carotid sinus and carotid bodies inhibits the activity of baroreceptor and chemoreceptor afferent nerves. Furthermore, NO synthase (NOS) is present in endothelial cells and in sensory nerves innervating the carotid sinus region. The major goal of this study was to determine whether overexpression of NOS in carotid sinus modulates baroreceptor activity. Rabbits were anesthetized, and adenoviral vectors (5 x 10(8) plaque-forming units) encoding genes for either beta-galactosidase (beta-Gal) or endothelial type III NOS (eNOS) were applied topically to the adventitial surface of one carotid sinus. In some experiments, the NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) was applied to the carotid sinus immediately after the vector. Four to five days later, baroreceptor activity and carotid sinus diameter were measured from the vascularly isolated carotid sinus of the anesthetized rabbits. Transgene expression was confirmed by X-Gal staining of beta-Gal and measurement of NOS activity by citrulline assay. The expression was restricted to the carotid sinus adventitia. Baroreceptor activity was decreased significantly, and the pressure-activity curve was shifted to higher pressures in eNOS-transduced (n = 5) compared with beta-Gal-transduced (n = 5) carotid sinuses. The pressure corresponding to 50% of maximum activity averaged 55 +/- 6 and 76 +/- 7 mmHg in beta-Gal- and eNOS-transduced carotid sinuses, respectively (P < 0.05). Decreased baroreceptor activity was accompanied by a significant increase in carotid diameter in the eNOS-transduced carotid sinuses (n = 5). l-NAME prevented the inhibition of baroreceptor activity and the increase in carotid diameter in eNOS-transduced carotid sinuses (n = 5). We conclude that adenoviral-mediated gene transfer of eNOS to carotid sinus adventitia causes sustained, NO-dependent inhibition of baroreceptor activity and resetting of the baroreceptor function curve to higher pressures.

Animals↗

Drainage of the prelymphatics of the brain via the adventitia of the vertebral artery.

Carbon particles injected into the cortex of the cerebellum of the rat were found in the Virchow-Robin spaces of the adjacent capillaries, and in the adventitia of the cerebellar artery, basilar artery and vertebral artery--both inside and outside the skull. They were also found in some portions of the deeper cervical lymph nodes. However, while tracers injected into the cerebral hemispheres are drained via the tissue channels in the adventitia of the internal carotid arteries, tracers injected into the cerebellar hemispheres are drained via those of the vertebral arteries.

Animals↗

The reactive adventitia: fibroblast oxidase in vascular function.

The vascular adventitia is activated in a variety of cardiovascular disease states and has recently been shown to be a barrier to nitric oxide bioactivity. Vascular fibroblasts produce substantial amounts of NAD(P)H oxidase-derived reactive oxygen species (ROS) that appear to be involved in fibroblast proliferation, connective tissue deposition, and perhaps vascular tone. However, the physiological and pathophysiological roles of the adventitia have not been extensively studied, possibly because of its location in large blood vessels remote from the vascular endothelium. In recent years, substantial information has been gathered on pathways leading to oxidase activation in smooth muscle cells and fibroblasts and the downstream signaling pathways leading to hypertrophy and proliferation. A clearer understanding of the molecular mechanisms involved will likely lead to therapeutic strategies aimed at preventing vascular dysfunction in diseases such as atherosclerosis, in which these pathways are activated.

Animals↗

The lamina adventitia is the major site of immune cell accumulation in standard chow-fed apolipoprotein E-deficient mice.

OBJECTIVE: Cells of adaptive immunity have been implicated in atherogenesis. Though substantial information is available on immune cells in atherosclerotic lesions of the lamina intima, cells in the lamina adventitia have received less attention. METHODS AND RESULTS: The composition of immune cells in the innominate artery and abdominal aorta was examined in young, adult, and old apolipoprotein (apo) E(-/-) and wild-type mice on standard mouse chow. In the innominate artery of apoE(-/-) mice, adventitial T cells increased at 32, 52, and 78 weeks exceeding those of the intima by 6-, 24-, and 85-fold. Single T cells dominated in young mice, later T/B cell clusters emerged, and lymphoid-like structures reminiscent of inflammatory follicles formed preferentially in the abdominal aorta of old mice. Follicles contained organized sets of immune response-regulating cells: Interdigitating dendritic cells, T cell effectors, proliferating B cells, and plasma cells. Adventitial T cell inflammation was associated with a marked increase in transcripts of the chemokine MIP-1alpha in the aorta but not in spleen or liver. CONCLUSIONS: Adventitial lymphocyte infiltration and formation of inflammatory follicle-like structures in the abdominal aorta of old apoE(-/-) mice point to the adventitia as a site of local adaptive immune reactions during atherogenesis in hyperlipidemic mice.

Age Factors↗

Vascular response to basic fibroblast growth factor when infused onto the normal adventitia or into the injured media of the rat carotid artery.

Immunohistochemical techniques localize basic fibroblast growth factor (FGF) in endothelial and smooth muscle cells of the common carotid artery. Thus, we studied the effect in rats of basic FGF infused for 14 days onto the adventitia or into the media in vivo. In untreated rats, the adventitial layer is uniform, and few vessels are observed in cross sections (mean +/- SEM is 0.351 +/- 0.16 capillaries/field at a magnification of x 480). Whereas saline infusion increases the mean number of vasa vasorum to 2.73 +/- 0.011 capillaries/field (p less than 0.01), basic FGF (1 ng/microliter/hr) increases the capillary number to 13.4 +/- 0.67 capillaries/field. The effects are local and restricted to the site of delivery; no cell proliferation is observed even 2 mm from the site of infusion. There is also no evidence of the infiltration of macrophages and monocytes. In an effort to determine the effect of basic FGF in the media, a small longitudinal (1-mm) incision was made in the adventitia, and saline or basic FGF (1 ng/microliter/hr) was infused for 14 days into the arterial wall. Under these conditions, basic FGF is a potent inducer of smooth muscle cell proliferation in the vascular wall as well as of new capillaries. In these instances, however, the capillaries formed are thick-walled. The results support the hypothesis that basic FGF may be contributing to the growth and maintenance of the vasa vasorum and of vascular smooth muscle cells.

Animals↗

The adventitia may be a barrier specific to nitric oxide in rabbit pulmonary artery.

To determine whether the adventitia that surrounds pulmonary vessels acts as a barrier specific to nitric oxide, special lucite chambers were constructed to measure the force of contraction of rabbit pulmonary artery rings in which the endothelial or adventitial surfaces could be preferentially exposed to nitric oxide (NO), carbon monoxide (CO), or sodium nitroprusside (SNP). Delivery of NO to the endothelial and adventitial surfaces of preconstricted vessels produced markedly different concentration-response curves with maximal relaxations of 89 +/- 3 and 11 +/- 9%, respectively. In contrast, relaxations induced by both CO and SNP did not differ significantly between endothelial and adventitial exposure to these agents. Placement of a layer of pericardium onto the endothelial surface eliminated relaxation to the endothelial delivery of NO but not to CO. We conclude that the pulmonary vascular response to NO displays a striking sidedness which is not observed either with CO, another gas of similar molecular weight, or with SNP, both of which cause relaxation by stimulating guanylate cyclase. The elimination of NO but not CO relaxations with a layer of pericardium may indicate that the adventitia acts as a barrier specific to NO. This directionality of effect provides evidence for a highly localized regulation of pulmonary vascular tone by endothelial cell NO and also indicates that extravascular NO may have limited access to pulmonary vascular smooth muscle.

Animals↗

Abundant progenitor cells in the adventitia contribute to atherosclerosis of vein grafts in ApoE-deficient mice.

Recent evidence indicates that vascular progenitor cells may be the source of smooth muscle cells (SMCs) that accumulate in atherosclerotic lesions, but the origin of these progenitor cells is unknown. To explore the possibility of vascular progenitor cells existing in adults, a variety of tissues from ApoE-deficient mice were extensively examined. Immunohistochemical staining revealed that the adventitia in aortic roots harbored large numbers of cells having stem cell markers, e.g., Sca-1(+) (21%), c-kit(+) (9%), CD34(+) (15%), and Flk1(+) cells (4%), but not SSEA-1(+) embryonic stem cells. Explanted cultures of adventitial tissues using stem cell medium displayed a heterogeneous outgrowth, for example, islands of round-shaped cells surrounded by fibroblast-like cell monolayers. Isolated Sca-1(+) cells were able to differentiate into SMCs in response to PDGF-BB stimulation in vitro. When Sca-1(+) cells carrying the LacZ gene were transferred to the adventitial side of vein grafts in ApoE-deficient mice, beta-gal(+) cells were found in atherosclerotic lesions of the intima, and these cells enhanced the development of the lesions. Thus, a large population of vascular progenitor cells existing in the adventitia can differentiate into SMCs that contribute to atherosclerosis. Our findings indicate that ex vivo expansion of these progenitor cells may have implications for cellular, genetic, and tissue engineering approaches to vascular disease.

Animals↗

Role of endothelium and adventitia on eugenol-induced relaxation of rabbit ear artery precontracted by histamine.

Eugenol (> or = 0.1 mM) inhibited the contractions induced by various stimulants, such as 90 mM extracellular K+ solution ([K+]0), histamine and noradrenaline in the rabbit ear artery. Inhibitory actions of eugenol occurred in a concentration-dependent manner, however, eugenol more dominantly inhibited the histamine-induced contraction than those induced by either 90 mM [K+]0 solution or noradrenaline. Removal of both endothelium and adventitia did not change the inhibitory actions of eugenol on the 90 mM [K+]0- and noradrenaline-induced contractions, however, attenuated those on the histamine-induced contraction. Chlorphenylamine abolished the histamine-induced contraction, but neither cimetidine, ranitidine nor thioperamide modified the eugenol actions on the contractions induced by histamine. Pretreatment with nitric oxide syntheses inhibitor NG-nitro-L-arginine (LNNA; 100 microM), but not soluble guanylate cyclase inhibitor methylene blue (MB; 10 microM), prevented endothelium/adventitia-dependent augmentation of the eugenol-induced relaxation on the histamine-induced contraction. When an intact tissue, but not an endothelium/adventitia-denuded tissue, was placed at the up-stream close to the other denuded preparation (test preparation), histamine-induced contraction observed in the test preparation tended to be augmented. Similarly, eugenol-induced relaxation was also augmented by the same treatment. Eugenol (0.3 mM) inhibited the excitatory junction potentials (EJPs) without hyperpolarization of the membrane. However, a high concentration of eugenol (1 mM) slightly hyperpolarized the membrane (ca. 5 mV). No transient enhancement of amplitude of EJP was recorded. These results suggest that eugenol may inhibit the histamine-induced muscle contraction directly, and the inhibition is augmented by the adventitia and endothelium partly by vasoactive substances, which were released from the adventitia/endothelium-derived substances in rabbit ear artery.

Animals↗

Angiotensin converting enzyme in the endothelium and smooth muscle cum adventitia of the normo- and hypertensive rat aorta.

Angiotensin converting enzyme (ACE) activity in the endothelium and smooth muscle cum adventitia of the normo- and hypertensive rat aorta was investigated. The aortic tissues of spontaneously hypertensive (SHR) rats, compared to those of the Wistar Kyoto (WKY) and Sprague Dawley (SD), contained significantly higher level of ACE activity. Expressed as mumole per min per mg total protein, the endothelium of the SHR contained 105 +/- 11 (mean +/- SEM) and those of the WKY and SD, 69 +/- 7 and 77 +/- 9, respectively. Similarly, the ACE activity in the smooth muscle cum adventitia were 97.6 +/- 8.2, 52.6 +/- 6.4 and 25.7 +/- 4.1 for the SHR, WKY and SD respectively. These results support our earlier assumption that the high level of ACE activity in the lung of SHR is a reflection of the increase in ACE activity of the blood vessels. However, our results and related findings of other investigators do not permit firm speculation as to whether the increase in ACE activity in the SHR is the cause or the result of hypertension in these animals.

Animals↗

Cerebrospinal fluid may nourish cerebral vessels through pathways in the adventitia that may be analogous to systemic vasa vasorum.

Cerebral blood vessels are devoid of vasa vasorum. Therefore, the authors have studied the microarchitecture of the adventitia of large feline cerebral vessels of the same size, in an effort of determine how the vessels are nourished. The cerebral vessels contain a rete vasorum in the adventitia that is permeable to large proteins and is in continuity with the subarachnoid space. This substructure may be analogous to the systemic vasa vasorum and may contribute to the nutrition of the cerebral arteries.

Animals↗

Vascular adventitia is a suitable compartment to transplant transduced vascular smooth muscle cells for ex vivo gene expression.

Vascular smooth muscle cells (VSMC) are ideal for systemic gene therapy because of their proximity to blood vessels and they have demonstrated long-term exogenous gene expression in vivo. However, the procedure generally followed to seed the transduced VSMC onto arteries denuded of endothelial cells usually induces stenosis and thrombosis, with a consequent high risk for use in humans. We demonstrate here that the vascular adventitia is a suitable place to introduce transduced VSMC and to secrete therapeutic proteins into the blood stream by a simple procedure, avoiding postoperative vascular complications. Transduced VSMC, with the retroviral vectors carrying the human growth hormone gene (hGH), were seeded into the adventitia of the rat abdominal aorta by single injection of a cell suspension. Based on the hGH and anti-hGH production in serum and on histological analysis of the removed aortas, we demonstrated hGH production over the 2-month experimental period. None of the animals used in the experiment showed stenosis, thrombosis, or other vascular or visible physiological abnormalities.

3T3 Cells↗

Large mediastinal teratoma originating from the aortic adventitia.

Many mediastinal tumors do not cause local symptoms, so they are discovered incidentally upon thoracic imaging. We present the case of a patient who had a large, mature, cystic, mediastinal teratoma. The primary tumor arose from the ascending aortic adventitia and was in a highly unusual location-the medial mediastinum. The teratoma, which was diagnosed in our patient on thoracic computed tomography for follow-up evaluation of empyema, was resected completely. To our knowledge, such a teratoma, arising from the adventitia of the ascending aorta in the medial mediastinum, has not previously been reported in the English medical literature. We review diagnostic methods and therapeutic approaches to such mediastinal tumors. We conclude that surgical resection is the method of choice for treating these tumors, because it enables radical therapy and tissue diagnosis after extirpation.

Adult↗

[Cystic degeneration of adventitia].

A description is presented of the cystic degeneration of the adventitia of the external iliac and femoral arteries. Numerous cysts in the adventitia compressed the arterial lumen and resulted in thrombotic occlusion. The histologic picture was similar to that of tendinous sheath ganglion. A list is given of cases already described with a discussion of the views concerning its aetiology and pathogenesis.

Cysts↗

[Cystic degeneration of the tunica adventitia of the popliteal artery].

INTRODUCTION: Adventitial cystic disease of the popliteal artery (PA) is an uncommon and unique entity characterized by a mucinous cyst located in the arterial adventitia. As the cyst enlarges, it provokes vascular compression with stenosis or occlusion, the first only during the knee flexion, and then in all leg position. Atkins and Key (1946) were the first who described this disease in the external iliac artery [1]. Eirup and Hiertonn (1956) described the disease in the PA, which is the place of its most common localization. The aim of the paper is the presentation of our 10 cases of PA adventitial cystic disease. PATIENTS AND METHODS: Ten patients with PA adventitial cyst were treated at the Institute of Cardiovascular Diseases of the Serbian Clinical Centre in Belgrade, over the period between 1978 and 1997. There were 9 males and one female patient, average age 42.7 years (31-62). Two patients were smokers, while all other atherosclerotic risk factors, including heart disease, were absent. The diagnosis was established using Doppler ultrasonography and angiography. The postoperative histological examination revealed PA adventitial cyst in all patients (Figure 1). In Table 1 are presented our patients. The patients 3 and 4 were admitted for acute ischaemia of the leg. In patient 3 Doppler indexes were 0.0, and transfemoral arteriography revealed segmental occlusion of the PA. All other arteries were unchanged. These findings suggested an unusual disease of the PA. During the operation the posterior approach to the PA was used, and intraoperatively the adventitial cyst was found. In patient 4 the tibioperoneal trunk, posterior tibial artery and PA were occluded. Therefore, the medial approach to the PA was used. After thrombectomy of the crural vessels, the popliteo-popliteal bypass procedure was performed. The PA resection by this approach was not possible. The ringed 6 mm PTFE graft was used for reconstruction because of inadequate saphenous vein. The patients 1, 2, 5-10 were admitted with disabling claudication discomforts. In patients 1, 2, 5, 6, 8, 9 popliteal and pedal pulses were absent, and Doppler indexes decreased. In patients 7 and 10 pedal pulses were palpable and decreased during the normal knee position, while absent during the knee flexion. During some maneuvers Doppler indexes significantly decreased. Transfemoral arteriography in patients 1, 2, 5, 6, 8, 9 showed segmental stenosis or occlusion of the PA, and for this reason the posterior approach to the PA was used. The PA adventitial cyst was found in all cases (Figure 2). In patient 7 angiography revealed a "hourglass" deformity of the PA, while in patient 10 "scimitar" sign was found. Both angiographic findings are characteristic of PA adventitial cyst. The posterior approach was carried out in all patients. In patient 2 only cyst aspiration has been performed, while in patients 7, 8, 9 aspiration and resection of the changed PA adventitia (Figure 3a, figure 3b). In patients 1, 3, 5, 6, 10 an occluded arterial segment was resected. The restoration of the flow observed after the end-to-end anastomosis in patient 1, and after interposition of the saphenous graft in other patients. After the operation, the contralateral leg was examined using Doppler ultrasonography in all patients. The Doppler indexes were significantly decreased in patients 1 and 5 during the knee flexion, but the patients refused the angiographic examination. The control examination consisted of physical examination, Doppler ultrasonography and sometimes angiography; it was carried out after 1, 3, 6 and 12 months, and then every year after the operation. RESULTS: There was no mortality among our patients in the early post-operative period. In patients in whom cyst aspiration was performed, claudication discomfort was decreased, and Doppler indexes were significantly increased. In patients with arterial resection and reconstruction (1, 3, 4, 5, 6, 10) the effect of the operation was simi

Adult↗